In many personal computer systems, information as to character shapes and the like is stored at, and supplied by, the printer. A wide variety of type styles and sizes is available and in general use. In order that each user be able to have the fonts that he or she deems desirable without the necessity of building an excessive amount of font data into each printer, replaceable font cartridges are commonly used, each cartridge containing the character information corresponding to a few fonts. When different fonts are desired, the existing cartridge is removed and a different one plugged in. Hence, a user need not purchase a large number of unwanted fonts in order to obtain the fonts he or she desires to use. Most printers in common use, however, have one or at most two receptacles for plugging in cartridges, which severely limits the selection of fonts available at any one time. This limitation is even more severe in practice than it appears, since commercially available font cartridges seldom utilize a large percentage of the font data address space capability of the printer font data bus. Also, since the manufacturers of font cartridges decide which combinations of fonts to put in font cartridges, it may not be possible for a user to have the selection of fonts he or she desires available on line at any one time, irrespective of how many cartridges are owned.
It is an object of the present invention to expand the on line font capability of printers used with personal computers by providing an expansion module for a font cartridge which permits installation of a user-specific selection of fonts in a printer which uses font cartridges as a source of character shape information.
It is a further object of the present invention to permit expansion of the number and/or variety of fonts available on line in a personal computer printer while utilizing previously purchased font cartridges.
It is a still further object of the invention to provide a font cartridge expansion module which can be used either in an expanded mode (in conjunction with a font cartridge) or used by itself (without expansion) as a stand alone font cartridge.
Yet another object of the invention is to provide a finger operated latching system for securing an expansion module to a font cartridge so that a font cartridge and attached expansion module can be conveniently inserted and removed from a printer as a unit.